Guide catheters are used in a variety of therapeutic and diagnostic medical procedures to facilitate insertion of instruments and implantable components. Guide catheters often comprise a rigid material or support structure to provide the torqueability and pushability characteristics that facilitate passage of the guide catheter to a particular site. With the stiffer material or support structure, the responsiveness of the distal portion of the guide catheter to manipulation of the proximal portion of the guide catheter typically improves. A flexible material, however, permits the guide catheter to navigate around tight bends and other hard-to-reach places. Although some guide catheters may be genetically configured for use with a variety of procedures, some guide catheters have a particular length, stiffness and distal tip shape adapted for access to a specific tissue or organ.